(This is my first instructable. There will be more pictures when I figure it all out.)
Perhaps you have a cast iron skillet that you just can't seem to season correctly, or maybe it's covered in rust, or both. You could scrub it forever with steel wool and get it 80% right, you could attack it with wire brushes and acid...or you could use electrolysis. Please be aware that this plan mixes ELECTRICITY with WATER and produces EXPLOSIVE GAS, so you really, really need to be careful.
* Rubbermaid-type waterproof container like you'd use to store clothing or christmas ornaments. Any size, just as long as it's big enough to contain the item laying flat.
* 4 Steel Junction Box Covers, no knockouts. Typically about 65 cents each.
* 4 Steel 8x32x2" machine screws, normally 99 cents a package
* 16 Steel 8x32 nuts. The package I got was 99 cents for 22 nuts.
* 4 feet of electrical wire, I prefer solid 12G. I pulled mine from a spare piece of 12/2 romex-type wire. 1 piece cut into 2, 2 foot lengths
* ~2-4 feet of crappy wire. Mine was 18G stranded, such as you can buy at Wal-Mart or an Autoparts store for a few dollars for a spool.
* Soldering iron or Butane Torch. I use a torch myself.
* Solder, flux core
* battery charger. Trickle will work, but will take about a bazillion years. You want at least 10A constant, such as you'd find in a car battery charger. (50A+ "Boost" mode works GREAT but normally will only run in 60-90 second pulses plus cooldown. Feel free to use a big charger if you have one that can throw this kind of power consistently.)
* Box of Arm and Hammer Washing Soda. NOT BAKING SODA. Washing Soda, normally found in the clothes detergent aisle. Also can be used for making your own clothes detergent for pennies a load.
* A scrap piece of wood (I used a 2x4) at least 6 or so inches longer than the skinny width of your waterproof container.
* 3/16" drill bit and a drill to make it work
* A larger drill bit---anywhere from 1/2" to 1", you'll only be drilling one hole in that 2x4.
* A pair of needlenose pliers or something like them.
* Water. Hot water works best.
* A fan to dilute the hydrogen that is expelled by the process
I had most of this stuff sitting around, I had to buy the steel box covers (These were the cheapest way I could find to buy skinny steel. You can use anything, really---but you want to maximize surface area.)
Place 4 box covers on top of each other so that all the holes line up exactly. Clamp them if possible. Wear gloves, because if they break loose while you're drilling, they will cut you.
Drill 4 holes through each cover using the 3/16" bit, approximately the same distance apart, somewhere near the middle. If you measure in about 1.5" from the corners of the metal, that's good enough. If you've got a ballsy enough drill, you should be able to drill through all pieces at once for 4 total sessions. If not, you can do them separately, just make SURE that the holes you're drilling line up EXACTLY with each other from piece to piece.
Grab any of the covers. Through each of the four holes, place one of the 8x32 steel machine screws. Onto each screw, now thread a nut. Tighten it as tightly as you can. Now, place the next cover onto the bolts, repeat with the nut. Repeat for all 4 pieces. It should be said here that you are welcome to use as many covers as you want, but 4 should be more than sufficient. You should now have 4 covers separated evenly by the nuts, with about 1" or so of bolt sticking out.
There are a jillion ways to do this. I personally stripped about 3" of the 18G stranded wire and wrapped it tightly around one of the extended pieces of machine screws, twisting tightly into the threads. Then use your torch or iron to very firmly solder the wire to the screw. You really can't use too much solder here, you need it to stick well. Go to town. Repeat for all 4 screws. You should now have 4 covers attached with 4 screws, each with a 12-18" pigtail of wire dangling from them.
Strip 2-3" from each of the dangling 18G wires. Strip 2-3" from the 12G wire. Place the wires parallel to each other, lining up the place where the stripping stops. (That is, where the insulation is equal.) Tightly wrap the 18G wire around the 12G wire. Now, use a pair of needlenose pliers to bend the 12G wire into a tight U, and then squeeze it onto itself. You're attempting to make a connection here that cannot easily be pulled apart. Now, use your torch and solder to permanently join the wire. Again, go bananas with solder. On the end of the 12G wire that is NOT soldered, strip about 3-5" of insulation from the wire.
At this point, you should go ahead and mix up your solution. If you can do this in the location where you will let the reaction happen, do so, because it will be happy. If not, move the tub to that location after filling but before putting the skillet in the tub.
Dump a bunch of washing soda into your tub. You don't need to supersaturate, but use a lot. At least 1 cup for every 5 gallons of water. Now start filling the tub with hot water. Doing it in this order makes it so you don't really have to stir, which is good if you're lazy like me. You're going to fill the tub so that there is about 5-8" of water ABOVE the edge of how high the skillet is off the bottom. Place the cast iron skillet in the container, bottom down (if you want to cure the bottom too, place it on spacer-blocks, pieces of wood would work fine). Double check that you've got enough water. There really isn't any such thing as too much, but it's going to make it hard to move and there's no reason to fill it more than I've said here. In fact, it may slow the reaction. Feel free to touch the water as much as you want, it will feel slippery and clean.
After you've got the level right, take your last 2' piece of 12G wire. Strip a BUNCH from one end, a good 6-8 inches. Wrap this firmly around the handle of your skillet in such a way that it can't possibly NOT be in contact. I put a few loops through the hole in the handle too, just to be sure. Strip about 3" away from the other end of the wire. Now place the skillet into the solution. I prefer to put the handle-end as far away from one side as possible and the other side right up against the wall, or a couple inches off of it. This is pretty much personal preference, but I find it makes step 6 easier.
This is the "artistic part." Your covers will now look pretty cool, kind of back-to-the-future, 4 covers to 4 wires to 1 wire. In the approximate middle of your 2x4" use a large-ish bit and drill a hole. 1/2" should be fine, but you can go bigger. Push the 12G wire from the covers up through this hole. Now, holding the wire in one hand and the 2x4 in the other, position the covers in the water above the skillet in as close to the middle of the skillet surface as you can get. Go ahead and let it touch the skillet as you position it perfectly. Now, pull the wire through the hole until the BOTTOM cover piece is hovering about 1/2" above the plane of the top of the skillet. Too close and they'll short, too far away and you'll slow the reaction. So, if your skillet has 2" high sides and a 3/8" thick bottom, you want your covers dangling ~3" off the bottom, centered over the skillet surface. Now wrap your wire around the 2x4 a few times (Make a clove-hitch if you think you're cool enough), this is done to keep the covers from slipping. If you're having trouble keeping them steady, use a wire-tie or a piece of string or even a wire anchor. The covers CANNOT slip and touch the surface of the skillet, or you'll wind up wasting time and electricity.
You're almost there! Check one last time that everything is as it should be. Now, turn on your fan blowing over and past the container, and/or do the whole operation outside, away from your house. Bend your 12G wires so that they push towards the same end of the tub. They can be near each other, they just can't touch each other. Following the instructions for your particular battery charger, connect the terminals. One of my chargers wants plugged in first, the other wants attached first. Do whatever yours wants. Make sure you've got it at the highest possible Amperage setting, being mindful that "Start" or "50A/Start" or "75A/Start" may overheat your charger if it doesn't have built in thermal protection. 10A is a nice safe place to let it sit for HOURS.
Black clamp MUST go on the SKILLET.
Red clamp MUST go to the covers.
Whatever is negative will get stripped, whatever is positive will get electroplated with what is stripped. Do it backwards and you'll just add have that much more to strip next time. If you've got carpentry clamps, feel free to clamp the charger clamps to the bin, however this shouldn't be necessary. Just make sure nothing can jostle the container and make them move. If either of the clamps on the charger should go in the solution....it will be electrolyzed and you don't want that to happen.
Basically as soon as you energize the circuit, you'll start to see bubbles. More bubbles = more reaction. Be aware that the bubbles are Hydrogen Gas (or perhaps more accurately Brown's Gas), regardless it's super explosive and not good to breathe in high concentration. Be mindful of sparks. This shouldn't be an issue if you're outside, but...still. It's hydrogen. No reason to recreate the Hindenberg in your basement.
Feel free to walk away for a while, although if you're like me you'll be back every 30 minutes to see what you can see. This setup generates enough bubbles that it can be hard to see what's going on. At any point you can cut power to the battery charger (I always give it about 30 seconds after that, but that's silly, it's not a capacitor!) and touch the water. To be extra safe you can disconnect one of the clamps. Feel free to pull your skillet out and examine it, just remember to reposition your covers before you turn it back on.
An hour is good, overnight is awesome. The crappier your skillet is, the longer it will take. Whenever you're satisfied, turn off the circuit, remove the skillet, rinse it and dry it well. You should IMMEDIATELY begin to reseason the skillet, as it is now SUPER VULNERABLE to rust.
The water is non-toxic, it's basically iron-enriched laundry water at this point. You can keep it for the next skillet, dump it in your yard or down the drain. It is not dangerous.
The nastier your skillet was, the more buildup will be on the covers. If you've got a bench grinder, you may be able to revitalize them, although you almost certainly won't get the nuts off. All the exposed copper will be electroplated in iron as well.If you did it right, you should be able to desolder the 18G wire from the screws and reuse it for your next job, assuming your covers are to covered in goo to reuse.
Notes: Stainless steel works better than just steel. It's also 4x as expensive. If you're going to do this a lot, invest in SS steel sheets and cut those. Also, basically any conductive metal will work, galvanized not so much.